On-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry for the analysis of protein biomarkers in biological fluids and food: A tutorial

The analysis by capillary electrophoresis (CE) of low abundant proteins in complex samples, such as biological fluids and food, is especially challenging, due to the poor concentration sensitivity of microscale separation techniques and the sample matrix complexity. In order to overcome these major drawbacks, microextraction sample preparation techniques based on on-line solid-phase extraction capillary electrophoresis (SPE-CE) are regarded as an excellent alternative for sample matrix clean-up and analyte preconcentration with minimum sample handling. In this study, we present, as a tutorial, a valve-free on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry (AA-SPE-CE-MS) method for purification, preconcentration, separation, detection, and characterization of intact protein biomarkers in biological fluids and food using as cases of study α‑synuclein (α‑syn), concanavalin A (Con A), and β-lactoglobulin (β-LG), which are related to Parkinson's disease and food allergy, respectively. This tutorial is not limited to the description of the analytical method, but it also provides ready-to-use preparation procedures for sorbent and microextraction devices, and introduces strategies to overcome undesired effects, allowing a straightforward implementation and optimum performance of AA-SPE-CE-MS, as a platform to develop further applications.